The present invention relates to a device for changing the status of a dual status magnetic electronic article surveillance marker.
Magnetic electronic article surveillance (xe2x80x9cEASxe2x80x9d) markers have been used for many years to protect items of value against theft. These EAS markers typically have a signal producing layer made of a low coercive force, high permeability magnetic material, and a continuous or segmented signal blocking layer made of a permanently magnetizable magnetic material. When the signal blocking layer is activated, it effectively prevents the signal producing layer from providing a signal that is detectable by an EAS detection system, and thus the EAS marker is deactivated. When the signal blocking layer is deactivated, then the EAS marker is activated, and an EAS detection system is able to detect the marker. EAS markers that may be activated and deactivated as described are sometimes referred to as xe2x80x9cdual-statusxe2x80x9d markers, to distinguish them from xe2x80x9csingle-statusxe2x80x9d markers that are always activated. Billions of dual-status EAS markers have been sold to date, and they protect assets such as library materials against theft around the world.
The devices used to activate and deactivate magnetic EAS markers are themselves magnetic. That is, they may include an array of magnets or an electric coil that produces a magnetic field of a desired intensity near a working surface, so that the EAS markers may be passed over that surface to selectively activate or deactivate the marker. Unfortunately, some devices used to change the status of a dual-status marker have the potential to harm magnetically-recorded media, such as videotapes. That is, magnetically-recorded media can be erased, garbled, or damaged by the presence of a magnetic field. Thus, when magnetically-recorded media are passed over a device to change the status of an EAS marker attached thereto, the device may damage the magnetically-recorded media. In view of the foregoing, it is desirable to provide a device for deactivating dual-status magnetic EAS markers that will not damage magnetically-recorded media such as videotapes.
Conventional activation and deactivation systems may reliably activate or deactivate EAS markers positioned along the spine of a book, for example, because the position and orientation of the marker relative to the magnetic field is generally known. With a compact disc, the EAS marker is likely to be positioned on the disc itself, and thus may be at any orientation in the X-Y plane relative to the case in which the disc is contained, and thus relative to the applied magnetic field. Conventional devices have compensated for this uncertainty by generating a more intense magnetic field, and although this increases the reliability of activation and deactivation, it can interfere with cathode-ray tubes (CRTs) located in the vicinity of the device. Furthermore, some patrons may perceive a health concern with elevated magnetic fields (whether justified or not), and thus may not wish to use such a conventional activation/deactivation device. Thus it would also be desirable to provide a device that overcomes these concerns.
Attempts have been made in the past to provide a device for changing the status of dual-status magnetic EAS markers without damaging magnetically-recorded media by controlling the intensity of the magnetic field within a short distance of a working surface, so that the marker may be deactivated or reactivated without damage to the magnetically-recorded media. That is, the magnetic field is strong enough at one distance (corresponding to the expected position of the EAS marker) to deactivate the marker, but is not strong enough at a second, greater distance (corresponding to the expected position of the magnetically-recorded media) to damage the magnetically-recorded media. These fields have generally been created using an array of individual magnets, or an open coil. Although this distance-dependent approach has met with some success, it requires the user to locate the EAS marker so that the EAS marker can be passed over the working surface in the intended manner. This normally requires that the magnetically-recorded media be removed from its case or container, which is time-consuming. Also, if for some reason the magnetic field above the working surface is greater than expected or designed, damage to the magnetic media can still result.
In one embodiment, the present invention overcomes these difficulties in the following manner. A magnetic field that is substantially uniform within an area of interest is produced at an intensity that is sufficiently high to reliably activate or deactivate the EAS marker, but sufficiently low to prevent damage to the magnetically-recorded media, such as videotape. Common videotapes, for example, may be damaged when exposed to magnetic fields of approximately 590 Gauss or more, and may show some negative effects when exposed to magnetic fields of 560 Gauss or more. On the other hand, many magnetic EAS markers require a field of approximately 275 Gauss to be reliably activated and deactivated. Accordingly, if a field that is substantially uniform within an area of interest is created, dual-status EAS markers can be reliably activated and deactivated without risking damage to the magnetically-recorded media to which they are attached.
In another aspect, the device of the present invention can be used to reliably change the status of a dual-status EAS marker attached to optically-recorded media such as a compact disc. The inventive device can provide a constant magnetic field within an area of interest that is sufficient to deactivate or reactivate the marker regardless of its orientation in the X and Y direction, while in at least one embodiment minimizing or eliminating any magnetic field effects to which a person is likely to be exposed while using the device.
In one embodiment, the device of the invention selectively produces magnetic fields of different intensity by changing the reactance of the LCR circuit, rather than by changing the voltage. This is more efficient and requires fewer components, thus enabling the electronic package to be smaller.
These and other aspects of the present invention, including the use of radio-frequency identification (xe2x80x9cRFIDxe2x80x9d) tags and interrogators, are described in much greater detail below.